The present invention relates to linear array display devices and is more particularly directed to a signal processing circuit for use therewith, i.e., a device to generate line segments from digital input data. One such type of linear array display device is a linear thermal array.
It is known in the art to fabricate thermal recording devices having imaging stylii arranged in a linear array. Such devices typically are comprised of a plurality of stylii which are formed by disposing electrically resistive material on an insulating substrate to form a plurality of individual stylus in a single row. These stylii are electrically connected to drive circuits of the type disclosed in co-pending U.S. Patent Application Ser. No. 79,760, filed Sept. 28, 1979, now abandoned, and assigned to the assignee of the present application. Each stylus is selectively energized by the drive circuits to produce Joule heat. When the stylii are brought into contact with or in suitable proximity with a thermal sensitive imaging medium, each energized stylus makes a mark on the medium. Specialized protection circuits may be employed to control the drive circuits in order to prevent thermal overheating or even thermal burnout. Such circuits are disclosed in co-pending U.S. Patent Application Ser. No. 72,542, now U.S. Pat. No. 4,246,587, and Ser. No. 72,544, now U.S. Pat. No. 4,271,414, both filed on Sept. 4, 1979, and assigned to the same assignee as the present invention.
The input data that is either directly printed through the drive circuits or processed through the above-mentioned specialized protection circuits prior to being printed must typically be in the form of digital input data. If the monitored input data to be printed is an analog signal, other processing circuitry is required to convert the analog signal into an appropriate digital signal, i.e., by use of an analog to digital (hereinafter A to D) converter. One such type of A to D converter that employs the single slope method of conversion is disclosed in co-pending U.S. Patent Application Ser. No. 146,696, filed May 5, 1980, now abandoned, and assigned to the same assignee as the present invention.
Since a linear array display device can print only dots or line segments, a need was recognized to have a circuit that would process the data converted by an A to D converter into dots and line segments that would be commensurate with the monitored analog input signal. One contemplated method of accomplishing this would be to use a micro-processor to generate a line segment based on the converted data from the A to D converter. However, micro-processor based circuits typically require peripheral circuitry which would be a more costly approach than if the same function could be accomplished by discrete circuitry. The prior art teaches line segment makers for use with CRT display devices that convert measured values into discrete values which are in turn displayed as single dots. Prior art devices that display dots present problems when the analog input signal is at high frequency or when there are several overlapping waveforms in that it would be obviously difficult to distinguish what one was looking at.